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| #include <bits/stdc++.h>
#pragma optimization_level 3
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")
struct PairHash {
inline std::size_t operator()(const std::pair<int, int> &v) const { return v.first * 31 + v.second; }
};
#define MAX_N 1010101
#define INF 987654321
#define EPS 1e-9
#define ll long long
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vall3 vector<array<ll,3>>
#define all3 array<ll,3>
#define all5 array<ll,5>
#define vall5 vector<all5>
#define vll vector<ll>
#define vi vector<int>
#define vs vector<string>
#define usll unordered_set<ll>
#define uspll unordered_set<pll, PairHash>
#define umll unordered_map<ll,ll>
#define vvs vector<vs>
#define vvll vector<vll>
#define all(a) begin(a), end(a)
#define rall(a) rbegin(a), rend(a)
ll __gcd(ll x, ll y) { return !y ? x : __gcd(y, x % y); }
using namespace std;
ll combs[MAX_N], mod = 998244353;
ll modpow(ll n, ll x) {
if(x == 0) return 1;
ll res = modpow(n, x>>1);
res = (res * res) % mod;
if(x & 1) res = (res * n) % mod;
return res;
}
ll combOf(ll n) {
if(combs[n] != -1) return combs[n];
if(n == 1) return 26;
return combs[n] = modpow(26, (n + 1) / 2);
}
bool canBuildPalindrome(string& s) {
ll n = s.length();
ll r = n / 2, l = r - (n & 1 ? 0 : 1);
while(r < n) {
if(s[l] < s[r]) return true;
if(s[l] > s[r]) return false;
l--, r++;
}
return true;
}
ll helper(string& s, ll p) {
ll n = s.length();
ll mul = s[p] - 'A';
if(n & 1 and p * 2 + 1 == n) return mul;
if(!(n & 1) and p * 2 == n) return 0;
return (mul * combOf(n - (p + 1) * 2) % mod + helper(s, p + 1)) % mod;
}
ll solve(string &s) {
return (canBuildPalindrome(s) + helper(s, 0)) % mod;
}
int main() {
ios_base::sync_with_stdio(0);
ios::sync_with_stdio(0);
cin.tie(0);
memset(combs, -1, sizeof combs);
ll tc = 1;
cin>>tc;
for (ll i = 1; i <= tc; i++) {
ll n;
cin>>n;
string s;
cin >> s;
cout<<solve(s)<<endl;
}
return 0;
}
|
